With the recent market demands for higher performance semiconductor devices, reduced product cycle time, and cost reduction, circuits in semiconductor devices have become finer and more multi-layered, and the diameter of the wafers used in manufacturing processes has become larger. In addition, manufacturing paradigm has been shifted from mass production in one item to small production in diverse items. With these trends, the type of cleaning apparatus has been changing from conventional batch immersion type (hereafter called batch type) to single-wafer spin cleaning type (hereafter called single-wafer type). The batch type approach generally processes about 50 wafers sequentially between a plurality of chemical solution baths, while the single-wafer type approach cleans wafers one by one by holding a wafer, spinning it, and spraying chemical solution to both or any desired surfaces of the wafer.
The new cleaning method using the single-wafer type has advantages over the batch-type. Some advantages of various embodiments are: preventing cross contaminations between batches or in a batch, keeping a higher level of consistency across the wafer, being easily applicable to small volume production because it consumes less chemical solution per one process, and requiring smaller footprint per one apparatus. Because of these advantages, the transition to the single-wafer type has been accelerated.
However, the single-wafer type also has some drawbacks. One problem is that one process bath is shared by a plurality of chemical solution processings in order to minimize footprint, thus it is required to make the environment in the bath fully adequate for each processing. Particularly, the chemical solutions and rinsing water that are used for wafer processing should be separated, and thus the consumption of required utility and cleaning chemicals has been increasing in conventional technology. Especially, a considerable amount of exhaust utility or exhaust power is required. This is because it is known that the instability in the exhaust utility that is required for the apparatus leads to particle generation or watermark generation during wafer processing. Because of these problems being inferior to the batch type, an urgent improvement is required.
Although various approaches have appeared to solve the problems, there is no decisive solution so far. In particular, energy saving of utility is a critical issue to be solved in the view of global environmental protection and is an issue of primary importance to the single-wafer type cleaning apparatus. Therefore, the purpose of the present invention is to reduce the required utility while maintaining the advantages of the single-wafer type cleaning apparatus. The invention also provides a technology by which the amount of required chemical solution can be reduced.
In the single-wafer type, when cleaning is performed in one bath using various different chemicals, the bath is generally partitioned horizontally or vertically in order to avoid the chemicals from mixing with each other.
FIG. 7A shows an example of a partitioned approach. A similar technology is disclosed, for example, in the Japanese Patent Application Laid-Open No. 028395/1993. As shown in FIG. 7A, a pot P, which is capable of separate collection, comprises more than two portions called ring canals K1, K2, and K3, each of which has an opening toward the central space of the pot. When viewed from the holding table H of a wafer W, the openings are horizontally divided. In the center of the openings, the holding table H is placed for holding and rotating the wafer W with holding tools. The relative position of the holding table H and the pot P is variable. In the ring canals K1, K2, and K3, drainpipes P1, P2, and P3 are formed for conveying the solutions collected inside the pot P to outside. To maintain the ring canals K1, K2, and K3 under a negative pressure, a ring-shaped space R which is connected to the exhaust utility EX, is placed outer side of the ring canals and the ring-shaped space R is connected to the ring canals K1, K2, and K3 through a plurality of exhaust holes H1, H2, and H3 respectively.
When the wafer W held above the holding table H is processed with cleaning solutions L1, L2, and L3, the cleaning solutions L1, L2, and L3 are supplied from nozzles N1, N2, and N3 respectively and dispensed toward the wafer W. Cleaning solutions L1, L2, and L3 are separately collected into desired ring canals K1, K2, and K3 by relatively moving either of the holding table H or the pot P. In this example, the pot P is stationary, and the holding table H moves.
The holding table H that holds the wafer W moves at the height of the ring canal K1 and is rotated. When the cleaning solution L1 is sprayed toward the wafer W, due to the rotation of the holding table H, the cleaning solution L1 is scattered to the ring canal K1, collected therein, and drained through the drainpipe P1. Then, the holding table H moves at the height of the ring canal K2. When the cleaning solution L2 is sprayed toward the wafer W, due to the rotation of the holding table H, the cleaning solution L2 is scattered to the ring canal K2, collected therein, and drained through the drainpipe P2. After that, the holding table H moves at the height of the ring canal K3. When the cleaning solution L3 is sprayed toward the wafer W, due to the rotation of the holding table H, the cleaning solution L3 is scattered to the ring canal K3, collected therein, and drained through the drainpipe P3. As mentioned above, a plurality of chemical processes can be performed and each chemical solution can be collected separately. In addition, during the operation of these processes, the ring-shaped space R is kept under a negative pressure by the exhaust utility EX, and all ring canals K1, K2, and K3 are kept under a negative pressure through the exhaust holes H1, H2, and H3.
With reference to FIG. 7B, a vertically partitioned approach is described in which the ring canals K1 and K2 are concentrically placed. A shield plate S moves relatively to the pot P with the purpose of changing the flow of the solution droplets and gas, which are scattered in the direction of the radius of the holding table H due to its rotation, to the direction of the rotation axis.
When the chemical solution L1 is sprayed from the nozzle N1, the shield plate S moves beforehand so that the ring canal K1 is placed on a level plane with the wafer W, changes the direction of the scattered chemical solution L1 and airflow, and conveys them into the drain D1. Then, when the chemical solution L2 is sprayed from the nozzle N2, the shield plate S moves beforehand so that the ring canal K2 is placed on a level plane with the wafer W, changes the direction of the scattered chemical solution L2 and airflow, and conveys them into the drain D2. As mentioned above, the chemical solutions L1 and L2 and the airflow caused due to the rotation of the holding table H are collected into the drains D1 and D2 respectively, and drained out of the pot P through the exhaust pipes P1 and P2. At this time, solution component and gas component are drained out together.
Depending on the conditions during the wafer processing, the rotational speed of the holding table H may be high. In such a case, the airflow caused due to the rotation becomes larger and solution droplets are scattered more widely, therefore, it is required to capture and collect them with the process chamber or pot having a larger diameter. In contrast, in the case the rotational speed is low, the airflow caused due to the rotation becomes smaller and solution droplets are not scattered widely, therefore, it is better collect them with the process chamber or pot having a smaller diameter. Considering these facts, the vertically partitioned type seems to be more appropriate.
However, the collection of processing solution in the above mentioned conventional processing apparatus has challenges as follows. In the horizontally partitioned approach shown in FIG. 7A, all the ring canals K1, K2, and K3 are always opened. Therefore, there is a high probability that when a process is performed using one of the ring canals, the chemical atmosphere of the ring canal is taken in through the openings of other ring canals. Because the wafer holding table H is rotated at a high speed in the center, a negative pressure is caused inside. Therefore, it is conceivable that there is a strong tendency for the chemical atmosphere to be taken in through the ring canals, which are not used for the process. This degrades the purity of the collected chemical solution and results in unevenness of chemical process and/or watermarks on the wafer. To avoid them, it is necessary to keep the ring canals under suction by a large amount of drawing air, which requires a large amount of exhaust utility. As a result, the apparatus itself becomes large and the cost for processing is increased.
In the case of the vertically partitioned approach shown in FIG. 7B, the drains D1 and D2 collect the chemical solutions L1 and L2 respectively, however, they also collect gas components, which are brought by the holding table H. Therefore, the drainpipes P1 and P2 should be connected to the exhaust utility EX. In collecting the chemical solution L2, the gas, which is brought concurrently with the chemical solution L2, flows through the space in which the drain D1 is opened. To avoid contamination therein, it is necessary that the holding table H should be rotated at a higher speed to fully scatter the solution droplets of the chemical solution L2. Accordingly, the ring-shaped opening K2 and drain D2 should have enough space to receive the airflow caused by the higher speed rotation and thus it is necessary to use the pot P having a larger diameter. Also required is the exhaust utility to keep the space under a negative pressure. In addition, it is quite conceivable that the steam of the chemical solution L1 from the drain D1 may concurrently flow out. To avoid it, it is necessary to prevent the stagnation or backflow of the chemical solution L1 by using a large amount of exhaust gas. Therefore, the exhaust utility should be increased and thus there exists the problems of upsizing apparatus and greater cost, as in the horizontally partitioned approach.